说明：  1)生成2KHz和8KHz的混合信号,使该信号通过上述滤波器,观察滤波前后的波形变化和频谱分布情况, 2) 在改信号中加入高
(1) generate the mixed signal of 2KHz and 8KHz to pass the filter, observe the waveform change and spectrum distribution before and after filtering, 2) add high to the modified signal.)